strike protection

7/29/2019 Strike Protection

1/30

Lightning Strike ProtectionByRoy B. Carpenter, Jr.

Mark N. Drabkin, Ph.D.

Lightning Eliminators & Consultants, Inc.6687 Arapahoe Road, Boulder, Colorado 80303 USA

800-521-6101 or 303-447-2828

Home Page Address: http://www.lightningeliminators.comInternet Address: [email protected]


2/30

Contents

INTRODUCTION...................................................................................................2

WHATS THE PROBLEM?...................................................................................4

Direct Effects ......................... ........................... ........................... ........................... ..............4Secondary Effects.................................................................................................................4Power Lines ........................... ........................... ........................... ........................... ..............5

HOW LIGHTNING WORKS ..................................................................................6

Mechanics of the Strike.........................................................................................................6Secondary Effects.................................................................................................................8

Electromagnetic Pulse ....................... ........................... ........................... .......................8Electrostatic Pulse ......................... .......................... ........................... .......................... 11Earth Currents ..............................................................................................................12Bound Charge...............................................................................................................14

LECS SOLUTION ..............................................................................................15

Risk Factors........................................................................................................................15Prevention System Options.................................................................................................16

Dissipation Array System (DAS)................................................................................16The DAS Ionizer .......................... ........................... ........................... .....................19Grounding System..................................................................................................20

Spline Ball Diverter System (SBDS) .....................................................................21Transient Voltage Surge Suppression (TVSS)...............................................................21

Electrical Substations .............................................................................................22Power Lines............................................................................................................22

In and On Buildings ......................... ........................... ........................... .................22The Surge Preventor Series ...................................................................................23Filter Network .......................... .......................... ........................... .......................... 24

DAS Performance Data.......................................................................................................24

CONCLUSION....................................................................................................27

SELECTED BIBLIOGRAPHY.............................................................................28


3/30

Lightning Strike Protection

Introduction

Struck by lightning is a metaphor for sudden, unpredictable

disaster. A large thunderstorm can produce over 100 lightning

flashes a minute, and even a modest storm cloud can generate the

energy of a small nuclear power plant (a few hundred megawatts).

Not all lightning strikes the ground, but when it does, that energy

can be devastating. For a telecommunications firm to be shut down

for hours or days due to equipment damage, or a chemical plant to

have fires started by lightning, is a costly and hazardous risk.

Until relatively recently, there was little that could be done to

minimize this risk. Lightning strikes when and where it will.

Traditional lightning protection has sought to collect and divert the

energy of a lightning strike into the ground. While this may avoid

some of the worst effects of a direct strike, it has some seriousdrawbacks.

None of the traditional systems are 100 percent effective, and all

suffer from the secondary effects related to the close proximity of

the electrostatic and electromagnetic fields. They are dangerous to

flammables, explosives, and electronics.

The unanswered question is, why collect the strike in the first place,

when strikes always create side effects that must be dealt with?

LEC has demonstrated that it is possible to eliminate the strike

altogether, thereby avoiding all of the risks.

Since 1971, LECs Dissipation Array System (DAS) has proven

its effectiveness as a system guaranteed topreventlightning from

striking the protected area. In chemical plants, nuclear power

plants, oil and petroleum facilities, and many other installations,

LECs systems have demonstrated that loss and damage fromlightning is completely preventable (see Table 1).


4/30

Table 1

DAS Historical Sample - Broadcasting

Yearly Outages

Before After

Years

History Location

12 NONE 19 Windsor, ONT

5+ NONE 16 Omaha, NE

4+ NONE 13 Fresno, CA

4 NONE 9 Winston, NC

15 NONE 8 St. Francis, SDmany NONE 12 Las Vegas, NV

8 NONE 14 Ft. Myers, FL

20 NONE 15 Durango, CO

25 NONE 12 Dayton, OH

many NONE 10 Puerto Rico

This overview presents a brief explanation of atmosphericelectricity, lightning phenomena and their associated problems.

With this as a background, LECs various methods of lightning

protection are described and case studies offered to show how

these methods have been put into practice1.


5/30

Whats the Problem?

There is no question about the hazards posed by lightning strikesand their associated effects. Fires, injury or loss of life, damage and

destruction of property, and the significant downtime and outage-

related revenue losses due to equipment damage all make lightning

a serious threat. While the direct effects of a strike are obvious, the

secondary effects can be just as devastating. This is especially true

for electrical power lines and facilities with sensitive electronic

equipment.

Direct Effects

The direct effects of a lightning strike are physical destruction

caused by the strike and subsequent fires. When a direct strike hits

a facility where flammable materials are present, the flammables

may be exposed to either the lightning bolt itself, the stroke

channel, or the heating effect of the lightning strike.

The petroleum industrys history provides ample evidence of the

destructive nature of lightning activity. Millions of dollars of

petrochemical products and facilities are destroyed each year by

lightning-related phenomena in many parts of the world, and lives

are lost when these facilities are ignited or explode. For example, in

the Nigerian fire of 1990, a 670,000-barrel tank was set on fire by

lightning. The tank full of light crude was lost, plus the tank itself,

even though the Nigerian tank was protected with a conventional

radio active system. Clearly, traditional protection systems are not

sufficiently effective.

It is true that the risk of loss of one tank of product is small. But it

is also true that preventing the loss of one tank and product in one

country will usually pay for the protection of all the storage

facilities in that country.

Secondary Effects

The secondary effects of a direct or nearby strike include the bound

charge, electromagnetic pulse, electrostatic pulse, and earth

currents. The bound charge (and subsequent secondary arc) is the


6/30

sphere of influence. These transients will cause arcing between

wires, pipes and earth. Again, arcs in the right place initiate both

fires and explosions.

Gases venting from stacks, not normally burning, will often be

ignited as the result of secondary arc effects. PPG of Lake Charles,

Louisiana, experienced this phenomenon at their hydrogen vent

stacks for years. When a Dissipation Array was installed, the

burning stopped.

The secondary effects are not always easily identified as to cause or

mechanism. Conventional protection will not influence any of thesesecondary effects other than to increase the risk of an event. Air

terminals collect strikes and encourage a stroke termination in close

proximity to flammable materials.

In addition, the trend toward micro-miniaturization in electronic

systems development brings an increasing sensitivity to transient

phenomena. Transients of less than 3 volts peak or energy levels as

low as 10-7Joules can damage or confuse these systems and theircomponents.

Power Lines

Power line voltage anomalies are the greatest source of destructive

and disruptive phenomena that electrical and electronic equipment

experience in day-to-day operations.

There are four basic sources of anomalies: lightning, the local

utility, your neighbors, and your own equipment. Each of these

creates its own form of anomaly. Of these sources, lightning is

obviously the greatest normal threat in terms of potential

destruction and disruptive phenomena. A direct strike to the power

line at the service entrance can cause significant damage inside

unprotected or improperly protected facilities. A facility adequately

protected against lightning is also protected against otheranomalies.

A further possibility is that related to Murphys Lawthe

unexpected, the unusual, or the impossible. For example, an

automobile struck a utility pole with a 220 kV overbuild line over a

4 160 kV li f di h l l Th 220 kV li


7/30

requiring replacement, repair, reprogramming, or rerun of the

program in progress. Any of these events can result in lost time and

money. All of these events can be totally eliminated with theappropriate power conditioning equipment, properly installed and

maintained. Most of these events can be eliminated through the

correct use of relatively inexpensive protection equipment.

How Lightning Works

Since the first awareness that lightning is an electrical discharge,

scientists and engineers have studied thunderstorms and lightningextensively (although protection against lightning has not changed

substantially since Benjamin Franklins time). While centuries of

study and new sophisticated instruments have greatly expanded our

knowledge, there is still much about these phenomena that is not

clearly understood. To understand how lightning protection works

and which system is most appropriate for different applications, an

overview of the phenomena is needed.2

Mechanics of the Strike

Thunderheads are electrically charged bodies suspended in an

atmosphere that may be considered at best a poor conductor.

During a storm, charge separation builds up within the cloud. The

potential at the base of the cloud is generally assumed to be about

one hundred million volts and the resulting electrostatic field about

10 kV per meter of elevation above earth. The charging action (or

charge separation) within the storm cell usually leaves the base of

the cloud with a negative charge, but in rare cases the opposite

seems true.

This resulting charge induces a similar charge of opposite polarity

on the earth, concentrated at its surface just under the cloud and of

about the same size and shape as the cloud (see Figure 1).

As a storm builds in intensity, charge separation continues within

the cloud until the air between the cloud and earth can no longer act

as an insulator. The specific breakdown point varies with

atmospheric conditions.


8/30

Figure 1: Charge Separation

Low intensity sparks called step leaders form, moving from the

base of the cloud toward earth. These steps are of about equal

length, and that length is related to the charge in the storm cell as

well as the peak current in the strike. These steps vary in lengthfrom about 10 meters to over 160 meters for a negative stroke. As

the leaders approach earth, the electric field between leaders

increases with each step. Finally, at about one step distance from

earth (or an earthbound facility) a strike zone is established, as

illustrated by Figure 2. A strike zone is hemispherical in shape, with

the radius equal to one step length. The electric field within the

strike zone is so high that it creates upward moving streamers from

earthbound objects. The first streamer that reaches the step leadercloses the circuit and starts the charge neutralization process.


9/30

When structures intervene between the earth and the storm cells,

the structures are also charged. Since they short out a portion of

the separating air space, they can trigger a strike because thestructure reduces a significant portion of the intervening air space.

Charge neutralization (the strike) is caused by the flow of

electrons from one body to the other, such that there is no resulting

difference of potential between the two bodies (see Figure 3). The

process creates the same result as shorting out the terminals of a

battery.

Figure 3: Charge Neutralization (Strike)

Secondary Effects

A flash is defined as the ionized channel resulting from the lightning

discharge; a stroke is one surge of current in that channel. There are

four separate secondary effects that accompany the flash. These

are:

Electromagnetic pulse (EMP) Electrostatic pulse

Earth current transients

Bound charge


10/30

with the rate dependent on the channel path impedance and the

charge within the cloud. The rate of rise of these current pulses

varies by orders of magnitude. They have been measured at levelsof up to 510 kA per microsecond. A practical average would be

100 kA per microsecond.

Transient currents flowing through a conductor produce a related

magnetic field. Since these discharge currents rise at such a rapid

rate and achieve peak currents in the hundreds of thousands of

amperes, the related magnetic pulse they create can be quite

significant. The resulting induced voltage (EMP) within anymutually coupled wiring can also be significant (see Figure 4).

Figure 4: Stroke Channel EMP

As the charges build up in the clouds, a downward step leader is

initiated at the bottom of the thunderclouds. As the downward step

leader approaches the ground, an upward step leader meets it, andthe return stroke occurs. A huge amount of charge accompanies

this return stroke, which acts like a giant traveling wave antenna

generating strong electromagnetic pulse waves. Therefore, lightning

EMP can propagate for a long distance and affect large areas (see

Table 2)


11/30

Table 2

Lightning Return Stroke Data

Return Current I 5 kA - 200 kA

di/dt 7.5 kA/s to 500 kA/s

Velocity 1/3 Speed of Light

Length (height of thunderclouds) 3-5 km above grade

Any elevated transmission/data line will also suffer from lightningEMP interference, regardless of the usual shielding. The lightning

EMP has a very wide spectrum, and most of its energy is in the low

frequency portion. Therefore, lightning EMP could penetrate the

shielding and interfere with the system.

The EMP also has a related secondary effect resulting from the

current flowing into the grounding system. In this situation, the

fast-changing current in time (di/dt) creates a magnetic field whichis now mutually coupled to any underground (within-ground)

wiring that passes nearby, over or parallel to any part of that

grounding system. Again, the mutual coupling results in the transfer

of energy (EMP) into the underground wiring (see Figure 5). That

energy may not always be harmful to the entering electrical service;

however, it will most likely be high enough to damage data circuits.


12/30

Electrostatic Pulse

Atmospheric transients or electrostatic pulses are the direct result

of the varying electrostatic field that accompanies an electrical

storm. Any wire suspended above the earth is immersed within an

electrostatic field and will be charged to that potential related to its

height (i.e. height times the field strength) above local grade. For

example, a distribution or telephone line suspended at an average of

10 meters above earth in an average electrostatic field during a

storm will take on a potential of between 100 kV and 300 kV withrespect to earth. When the discharge (stroke) occurs, that charge

must move down the line searching for a path to earth. Any

equipment connected to that line will provide the required path to

earth. Unless that path is properly protected, it will be destroyed in

the process of providing the neutralization path. This phenomenon

is known as the atmospherically induced transient. The rising and

falling electrostatic voltage is also referred to as the Electrostatic

Pulse (ESP). (See Figure 6.)

Figure 6: Electrostatic Pulses


13/30

A vertically erected metallic object immersed in these static electric

fields, especially one having a sharp point, has a considerable

potential difference with respect to ground. If the object is notgrounded, it can cause sparks and in some hazardous locations

ignite fire or upset sensitive electronic equipment.

Earth Currents

The earth current transient is the direct result of the neutralization

process that follows stroke termination. The process of

neutralization is accomplished by the movement of the charge along

or near the earth's surface from the location where the charge is

induced to the point where the stroke terminates. Any conductors

buried in the earth within or near the charge will provide a more

conductive path from where it was induced to the point nearest the

stroke terminus. This induces a voltage on those conductors that is

related to the charge, which is in turn related to the proximity of the

stroke terminus.

Figure 7: Earth Current Transients

Thi i d d lt i ll d th t t i t It ill b


14/30

The termination of a return stroke on ground may cause the

following effects:

1. It may cause arcing through the soil to an adjacent gas pipeline,cable, or grounding system. (A 50 kV/m breakdown gradient is

usually assumed. For example, the foot resistance of a power

tower is 10 Ohms, the return stroke current is 200 kA, and the

minimum separation distance is 40 meters.)

2. Surge current may be coupled by soil to the existing electronicgrounding system, which causes a non-uniform Ground

Potential Rise (GPR) distribution in the ground system. Forexample, two buried 10 meter ground wires with a grounding

resistance of 31.8 ohms are separated by 5 meters. As a 75

Ampere current is injected into one of the ground rods, the

other rods will have a voltage rise of approximately 188 volts.


15/30

Bound Charge

The most common cause of lightning related petroleum product

fires is the phenomenon known as the bound charge and resulting

secondary arc (BC/SA).

To understand the risk of the BC/SA, it is necessary to understand

how the bound charge is formed and how the secondary arc results

in a fire. The storm cell induces the charge on everythingunder it.

That charge (ampere-seconds) is related to the charge in the stormcell. Since petroleum products are usually in a conductive metallic

container, that container and everything in it takes on the charge

and related potential of the local earth. Since the charging rate is

slow, the product will take on the charge as well as the tank.

The earth is normally negative with respect to the ionosphere.

When a storm cell intervenes between the ionosphere and earth, the

induced positive charge replaces the normally negative charge witha much higher positive charge. The container (tank) is at earth

potential, which is the same as the surroundings, positive before the

strike, but instantly negative after the strike.

The secondary arc results from the sudden change in charge (20

microseconds) of the tank wall and the unchanged state of the

contained products charge.

Grounding will have no significant influence on the potentialBC/SA phenomenon. Conventional lightning protection cannot

prevent the bound charge/secondary arc because there is no

discharge path available.


16/30

LECs Solution

Since 1971, LECs engineers have developed specialized expertisein the field of lightning protection. While traditional lightning strike

protection methods may be adequate for some installations, when

more complete protection is needed, LEC offers systems designed

to meet the most exacting requirements. Where the standard

configurations are not sufficient, LEC offers consulting and design

services to create custom systems that will solve the most difficult

protection problems.

Engineering an appropriate solution is more complex than simply

putting up a lightning rod. Each site is evaluated for risk factors,

geography, soil type, and many other parameters before a

protection plan can be implemented. For many reasons, there can be

no one size fits all solution to lightning strikes.

Risk Factors

The Keraunic number (lightning days per year), or isokeraunic

level, is a measure of exposure rate. The higher the Keraunic

number, the greater the stroke activity encountered in that area. In

the United States this number varies from a low of 1 to over 100. In

other parts of the world, it is as high as 300. There is an average of

30 storm days per year across the United States, and many strokes

occur in a single storm. Studies have shown that for an average

area within the USA there can be between eight and eleven strokesper year to each square mile. Within the central Florida area, the

risk is increased to between 37 and 38 strikes per square mile per

year.

Structural characteristics such as height, shape, size, and orientation

also influence this risk. For example, higher structures tend to

collect the strokes from the surrounding area. The higher the

structure, the more strokes it will collect. High structures will alsotrigger strokes that would not have otherwise occurred. Further,

since storm clouds tend to travel at specific heights with their bases

starting at five to ten thousand feet, structures in mountainous areas

tend to trigger lightning even more readily.


17/30

Prevention System Options

Since different facilities have different kinds of problems with

lightning, it is important to understand the capabilities and

limitations of each type of protection system. In most cases, one or

more of LECs products can be adapted to solve any lightning

protection problem. The following discussion briefly outlines

features of the static ionizer, the Ground Current Collector (GCC),

and various types of Transient Voltage Surge Suppression (TVSS).

For more detailed information on any of these products, please callLEC.

Dissipation Array System (DAS)

Lightning is the process of neutralizing the potential between the

cloud base and earth. Any strikeprevention system must facilitate

this process slowly and continuously. The Dissipation Array System

(DAS) has been designed to prevent a lightning strike to both the

protected area and the array itself. The primary system components

are the DAS Ionizer, the Spline Ball

Diverter System, and the

Chem-Rod

Grounding Electrode. Some or all of these may be

used in designing a particular protection system (see Figure 8).

Concentrated

Space Charge

Charged Storm Cell

Accumulated

Space Charge

Protected Area

Ground Charge CollectorDissipation Array

(Ionizer)Storm Induced

Charge

(Electrical Shadow)


18/30

To prevent a lightning strike to a given area, a system must be able

to reduce the potential between the site and the storm cloud cell, so

that the potential is not high enough for a stroke to terminate withinthe area. That is, the protective system must release, or leak off, the

charge induced in the area of concern to a level where a lightning

stroke is impractical. (Charge induction comes about because of the

strong electric field created by the storm and the insulating quality

of the intervening air space.)

Atmospheric scientists have found that much of the storms energy

is dissipated through what is called natural dissipation, which is

ionization produced by trees, grass, fences and other similar natural

or man-made pointed objects that are earthbound and exposed to

the electrostatic field created by a storm cell. For example, a storm

cell over the ocean will produce more lightning than the same cell

over land, because the natural dissipation of the land will reduce the

storms energy. Consequently, a multipoint ionizer is simply a more

effective dissipation device, duplicating nature more efficiently.

The point discharge phenomenon was identified over one hundred

years ago. It was found that a sharp point immersed in an

electrostatic field where the potential was elevated above 10,000

volts would transfer a charge by ionizing the adjacent air molecules.

The Dissipation Array System is based on using the point discharge

phenomenon as a charge transfer mechanism from the protected site

to the surrounding air. The electrostatic field created by the storm

cell will draw that charge away from the protected site, leaving thatsite at a lower potential than its surroundings (see Figure 9).


19/30

Figure 9: Point Discharge as a Transfer Mechanism

A second phenomenon that adds to the protection provided by the

DAS is the presence of a space charge. This charge develops

between the protected site and the storm cell and forms what may

be considered a (Faraday) shield. The ionized air molecules formed

by point discharge are drawn above the ionizer where they slowdown and tend to form a cloud of ionized air molecules (see Figure

10).


20/30

Figure 10: The "Space Charge" Effect

The DAS Ionizer

The DAS Ionizer is a multipoint device. It is designed to efficiently

produce ions from many points simultaneously. As the electrostaticfield increases, a single point will create streamers and encourage a

strike. In contrast, the multipoint ionizer starts the ionization

process at a somewhat higher potential; but as the potential

increases, the ionization current increases exponentially. Since these

ions are spread over a large area, no streamers are generated. In

extreme situations, a luminous cloud of ions is produced, causing a

momentary glow around the array and a sudden burst of current

flow.

The ionizer assembly is very sensitive to a number of design

parameters, some of which can be reduced to formulation, others

which cannot. These factors include size, shape, elevation, point

shape point height above the array face point spacing range in


21/30

Grounding System

The ionizer assembly alone, of course, is not sufficient. The system

must be grounded. The Ground Current Collector (GCC) providesthe source of charge to keep the ion current flowing through the

array and discharge the site. The GCC is designed to provide an

electrically isolated or floating ground subsystem for the protected

area with respect to the earth. Since the induced charge created by

the storm is at the earths surface, that portion of the earths surface

containing the facilities to be protected is usually surrounded with

the GCC. The GCC is normally composed of the Ground Current

Collector wire or copper tubing buried to a depth of about 25centimeters and short ground rods along the GCC at intervals of

about ten meters. The enclosed area may be integrated by a net of

cross conductors which also connect surface structures and the

grounding system.

LECs Chem-Rod Grounding Electrode is an ultra-efficient low

surge impedance grounding system. It provides the perfect low

resistance interface with true earth by continuously conditioning thesurrounding soil, using specially formulated mineral salts evenly

distributed along the entire length of the electrode. It is so efficient

that one Chem-Rod can replace up to ten conventional grounding

rods. The design of the Chem-Rod insures a stable, efficient system

that is virtually maintenance free.

As the charge moves into the area, it first interfaces with the GCC

which provides a preferred path for the charge from this point ofinterface to the dissipater or ionizer assembly by means of the

service wires, thus essentially bypassing the protected area. The

current flow thus created through the surrounding surface soil

causes a small voltage drop across that soil resistance. Thus, the

electrically integrated, isolated island established by the GCC is

reduced to a lower potential than its surroundings. The short

ground rods give the island enough depth to ensure collection of

any charge induced within the area of concern.

The Charge Conductor function provides a direct, low impedance

path from the GCC to the ionizer. In contrast to a lightning rod

system, these wires carry low current levels over the shortest path

possible and are selected more for structural integrity than for


22/30

The current flow from the ionizer through the air spaceabove it reduces the potential of the protected site and

facility with respect to its surroundings by draining thecharge from the protected area and transferring it to the air

molecules.

The presence of free ions or space charge between the

protected facility and the cloud structure forms a type of

Faraday shield between them, thus providing isolation for

the facility from the storm clouds static field.

Spline Ball Diverter System (SBDS)

LEC has also addressed the market for hybrid ionizers, which

combine the features of the ionizer with those of the air terminal.

This had led to the development of two products:

The Spline Ball Ionizer

(SBI) Module

The Spline Ball Terminal

(SBT

) ModuleBoth of these units are UL listed as air terminals, and both qualify

as ionizer modules. The multiple points make them an ionizer. The

proper spacing of points assures optimum ionization current before

it switches to the collector mode. They also qualify as air

terminals under UL96A, and therefore are usable as such in any

NFPA78-based system. Both Spline Ball assemblies are made up of

about 100 points each, which when deployed, present points set in

all 360 degrees in azimuth and about 200 degrees in elevation. As a

result, regardless of the orientation of the storm-related electric

field or an incoming leader, many ionizer points will be oriented

directly toward it and ready to transfer the charge rapidly.

These forms of ionizer modules support a wide variety of

applications. When enough of these modules are used to replace

conventional air terminals, this converts a conventional collector

system to a preventor system.

Transient Voltage Surge Suppression (TVSS)

As mentioned earlier, voltage line anomalies are the greatest source

of destructive and disruptive phenomena that electrical and


23/30

Electrical Substations

Surge suppression is a key element in the design of electrical

substations. The effectiveness of this subsystem will determine theBasic Insulation Level (BIL) requirements for the transformer and

related components. Transformers are the major cost factor in the

substation, so reducing the substation BIL requirements can have a

major impact on both cost and risk.

The BIL requirements are primarily related to the risk of incoming

surges or transients on the transmission lines. A close-in lightning

strike (within a kilometer or so) is the limiting case. To eliminatethe risk of fast-rising high current surges, two protection system

characteristics are required:

prevent direct strikes to any operational component withinthe substation.

prevent the passage of fast-rising, high-current surges.

Power Lines

Two classes of protectors are used to protect power lines against

lightning related anomalies:

Parallel Protectors are installed between phaseconductor(s) and ground (or neutral). They may include gas

tubes, metal oxide varistors, and avalanche diodes, used in

some parallel configuration. Often more than one device is

used. The positive benefits are that they are easy to install

and relatively inexpensive, but they typically involve some

compromises in performance.

Series Hybrid Protectors are installed in series with thephase conductors, with several parallel devices used to

dissipate the surge energy and limit the peak voltage. Themajor benefit is performance. By inserting a series inductor

in the power line, a high impedance at mid-range is set to

the frequency of the lightning related impulse (average

equals 1 MHz). This expedites turning on the primary

elements shunting the bulk of the surge to ground and


24/30

to which electronic equipment would be exposed in a field

environment, depending on their installation location. This standard

was revised in 1991 to reflect the effects of location on systemexposure. For example, a product in Florida (number of lightning

days per year = 100) would not have the same exposure risk as the

same product would have in California (number of lightning days

per year = 5).

When testing any product, such as a computer or a surge protector,

it is imperative that the proper tests be performed. Most engineers

will only think of a surge existing either hot-to-ground or hot-to-

neutral. In reality, a surge can be induced in all four modes: hot-to-

ground, hot-to-neutral, neutral-to-ground and hot-and-neutral-to-

ground. For example, if a standard plug-in surge protector is only

providing hot-to-neutral protection, the device is vulnerable to

impulses applied on the other modes. When reviewing

specifications on plug-in surge protectors, be careful to check that

all modes are protected.

The IEEE standard separates the impulse tests by location, definedas Category A, B, and C. Category C is for service entrance

installations. This includes any device installed outside the building

or as the power enters the building near the service disconnect, or

for runs between the meter and distribution panel. Category B

includes major feeder and short branch circuits, such as distribution

panels more than 30 feet inside the building, or lines that are run for

heavy appliances. Category A includes long branch circuits and alloutlets more than 30 feet from Category B with wire size ranging

from #14AWG to #10AWG.

NOTE: All electronic equipment surge suppressors must be

evaluated based on installation location.

The Surge Preventor Series

LECs surge suppression devices include all modes of protection:

SB04 (any voltage, Category C) - wye or delta for electricalservice entrance. These provide protection from line to

ground (earth) for wye connected systems or line to line for

delta configurations There are also special options for


25/30

Filter Network

The LEC Filter Network is a true power conditioning module that

accomplishes each step of the conditioning process in the mostenergy-efficient and cost-effective manner. First, series hybrid surge

protection is installed, then broad band filtering, and finally noise

limitation, in this sequence. This staged filtering concept provides

state-of-the-art performance. All of these filtering functions are

provided: line-to-line, line-to-neutral, and neutral-to-ground

(common mode and normal modes). There is not a more effective

device on the market today, nor can there be. This is the result of

designing for worst-case conditions and including Mr. Murphy inthe requirement analysis.

DAS Performance Data

Performance data is significant since it is the real indication of the

systems value. Performance data in these case histories is of the

go/no-go type (strikes or no strikes). The most valuable data of this

type is where there was a prior history of many strikes and thennone after installation of the LEC Dissipation Array System. The

longer the post-installation period, the better.

The statistics of the Dissipation Array Systems performance permit

a good estimate of reliability:

First, using the data as is and disregarding the fact thatfailed systems have been corrected, system reliability is

better than 99.7% in terms of system-hours.

Second, taking into account the impact of the retrofit workand resulting performance, the system reliability is in excess

of 99.9% in terms of system-hours.

These statistics provide formal assurance of the Dissipation Array

Systems reliability. However, the spectacular testimonials fromcustomers suffering from a long history of lightning losses who

have an immediate reduction to zero losses after the Array

installation are perhaps more persuasive. The following are some

relevant case histories.


26/30

outages per year due to lightning strikes to the towers. The

isokeraunic level for this area is about 31.

In November, 1972, LEC installed disc-shaped Ionizers. Thesesystems have been functioning since that time without any outages

or known lightning strikes. At one time, dissipation current

measurements were made and current flows of up to 20

milliamperes were noted by the stations chief engineer.

WBBH-TV, Fort Myers, Florida, is a television station serving that

area of Florida. Its antenna is mounted on a tower with a total

height of well over 300 meters. The isokeraunic level in that area isabout 100. The tower or antenna had been struck an average of 48

times per year resulting in damage and loss of air time on many

occasions. In 1975, LEC was asked to install a Dissipation Array

System. A Trapezoid Array was subsequently installed, and no

strikes or outages have been noted since that time. The customer

rebuilt the transmitter and tower in mid-1980, and a new DAS was

installed at that time. The no-strike record continues.

KLAS-TV, Las Vegas, Nevada, is of interest for two reasons: its site

situation, and its high former strike record. Physically, there is a 28-

meter antenna atop a 62-meter tower resting on a rock pile and no

soil cover in the area. The stones had to be moved to set the GCC

in place, as there was virtually no grounding. Prior to the Array

installation, the station was off the air any time there was lightning

activity in the area, five or six times a year. In 1974, LEC installed

an early form of Trapezoid Array. The station has never been offthe air due to lightning activity since that time.

ThePPG Chemical Plant, Lake Charles, Louisiana, is in an area

where the isokeraunic number is in the 70s. The plant produces

chlorine for commercial use. In the process, it off-gasses pure

hydrogen. Since the plants inception, nearby lightning strikes (not

to the site) would cause the hydrogen stack to light off due to the

significant change in the electrostatic field. The cause is usuallyreferred to as the bound charge and the secondary arc.

A DAS was installed on the new cells in 1979; later, two more were

protected. PPG people noted that not only were there no lightning

strikes to those areas, but the stacks were no longer ignited by


27/30

the main plant. Estimates for the stroke hazard range from two to

five times each year. Plant history reveals many lightning strikes to

the stack each year and related losses. A Dissipation Array System

was installed with three dissipators in 1976 to protect the whole

plant and related substation. No strikes have been recorded since

the installation was completed.

Federal Express Corporation, Memphis, Tennessee, first

contracted with LEC in 1982. Since that time, LEC has been

awarded over 40 contracts to protect their facilities. The largest

protected site is on the Memphis International Airport. LEC has

protected about three square kilometers of their sort facilities. By

any reasonable estimate, that facility should have been struck up to

20 times each year. No strikes have reached that area since 1982.

The corona effect is seen frequently and lightning continues all

around the site, but none within the protected area.

Union Camp Paper Company, Franklin, Virginia, installed the LEC

Dual Dissipater System (DDS) on a 13.8 kV power line feeding

pumps about three miles from the plant. The basic insulation level(BIL) was far too low for that line, and it tripped out during nearly

every storm before the installation of the DDS. Across the road

following the same path was a second line performing the same

function, but with a much higher BIL. It had been tripping out an

average of about three times per year for well over 10 years. It

remained unprotected. After the DDS installation on the lower BIL

line in 1987, there were no trip-outs from lightning. The other linecontinued to average three per year. There is no better test, and no

better proof of performance.


28/30

Conclusion

The risks from lightning are real, and traditional lightningprotection devices do not adequately cover all the risks. The

secondary effects which cause much of the damage are in fact

increased by collecting strikes.

LEC has developed proven technologies which can eliminate

lightning strikes from a protected area and protect against the

secondary effects of lightning where the facility is not completely

protected. If a lightning strike could put a facility out of business,or even out of action for a few hours, consider whether the cost of

preventing all future risks from lightning would not easily offset the

cost of installing one of LECs lightning elimination systems. It is

inexpensive insurance.


29/30

Selected Bibliography

Carpenter, Roy B. Lightning Prevention for Transmission and Distribution Systems,

American Power Conference, Chicago, IL, Vol. 49, 1987.

.... Lightning Strike Protection, Criteria, Concepts and Configuration, Report No. LEC-

01-86, Revised 1993.

.... New and More Effective Strike Protection for Transmission Distribution Systems,

1992.

Chalmers, Alton. Atmospheric Electricity, Pergamon Press, 1967.

Davis, Charles. Lightning and Fiber Optics, Transmission and Distribution, World Expo

92, Indianapolis, IN, 1992.

Eriksson, A. J. The Incidence of Lightning Strikes to Power Lines, IEEE Transactions

on Power Delivery, 3 July 1987.

Golde, R. H. Lightning Performance of High Voltage Distribution Systems, Proceedings

of the IEEE, 113 No. 4, April 1966.

Grzybowski, Stan. Effectiveness of Dissipators Used for Lightning Protection on 115 kV

Distribution Lines, (Rev. 1) Final Report dated Jan. 1992.

Lightning Protection Manual for Rural Electric Systems, NRECA Research Project 82-5,

Washington, DC, 1983.

Merrit, S. Design Charts to Relate Transmission Line Parameters to Flashover

Probability, Union Camp Paper, Franklin, VA, 1988.Uman, Martin. The Lightning Discharge, Academic Press, 1987.

Williams, Earle. The Electrification of Thunderstorms, in The Enigma of Weather,

Scientific American, 1994.


30/30
http://lec%20papers%20graphic%20copy.pdf/

strike protection

Documents